1. Field of the Invention
This invention generally relates to an image forming device, such as a copier, a facsimile and a printer, and more particularly to an image forming device which is provided with a developing device for developing a latent image on an image support object, as well as with a powder storing unit for storing powder for image formation to be supplied to the developing device.
2. Description of the Related Art
An electrophotographic printing system is one of image forming systems and many copiers, printers and facsimiles are provided as image forming devices using the electrophotographic printing system.
In the electrophotographic printing system, an electrostatic latent image is formed by exposure of a uniformly charged surface of a photoconductor (which is an image support object) to optical writing, etc. This electrostatic latent image is visualized using either a toner of a two-component developing agent in which a magnetic carrier and a toner are mixed or a one-component developing agent in which both are unified, and the visible image is transferred to a recording medium so that the copy image is obtained.
The developing agent used for visible image processing is consumed in accordance with performance of the visible image processing. When the consumed amount exceeds a predetermined amount, the supply of a developing agent to the image forming device is needed.
For example, in the case of the two-component developing agent, the amount of the toner is decreased with time, the density of the toner in the developing agent in the developing device falls. As a result, a desired image concentration is no longer obtained. To avoid this, a toner supplying part is provided in the developing device of the image forming device so that, when the toner density in the developing agent is below a predetermined value, the toner is supplied to the developing device, and the condition that the toner density in the developing agent is stabilized is maintained.
The toner supplying part is provided in the developing device to store a predetermined amount of toner, and supplies the toner to the developing agent according to change of the toner density in the developing agent.
The size of the toner supplying part provided in the developing device is usually made comparatively small in order to prevent enlargement of the image forming device. Generally, in the case of the developing device of the above-mentioned structure, when the toner stored in the toner supplying part is consumed completely, exchange of the toner supplying part will be performed by taking the toner supplying part out of the developing device.
However, at the time of exchange of the toner supplying part, operation of the image forming device is suspended temporarily, and the useless time to stop the image formation operation is required for the exchange work and the restart of the image forming device.
It is desirable to prevent such situations and to shorten the operation stop time of the image forming device. To attain this, there is proposed a developing agent supplying device in which a toner container part adapted for storing a comparatively large amount of toner is provided, and this toner container part is connected to a developing device. In this developing agent supplying device, the toner is supplied in accordance with the amount of the toner remaining in the toner supplying part provided in the developing device. For example, refer to Japanese Laid-Open Patent Application No. 61-188564.
However, when the toner storing unit having a large capacity for storing toner is used, the toner stored inside may be condensed, and there is a problem that it is difficult to smoothly transport the toner to the developing area.
To obviate the problem, Japanese Laid-Open Patent Application No. 2002-139902 discloses a toner supplying device in which a toner storing container is provided at its lower edge with an opening, and a shaft-like connector is provided so that the connector is detachably attached to the toner storing container through the opening in accordance with attachment of the toner storing container to the image forming device body.
In the toner supplying device of Japanese Laid-Open Patent Application No. 2002-139902, the toner stored in the toner storing container is supplied to the developing device through the connector. In the connector, a toner passage through which the toner supplied to the developing device passes is provided, and an air passage which communicates with an air supply unit is connected to an intermediate part of the toner passage.
Namely, in the method of Japanese Laid-Open Patent Application No. 2002-139902, air is supplied from the air pump (air supply unit) to the toner storing container, and it is possible to keep the fluidity of the toner in the toner storing container. And the air supplied through the air passage is not easily returned back to the toner exhaust part in the downstream direction, and it is possible to prevent occurrence of the toner clogging in the transfer tube.
However, in the method of Japanese Laid-Open Patent Application No. 2002-139902, the fluidity of the toner existing near the air exhaust outlet in the toner storing container is maintained, fully secured, but a sufficient amount of air is not supplied to the toner existing at the location distant from the air exhaust outlet. The toner existing at the location distant from the air exhaust outlet may be condensed. Especially, when the capacity of the toner storing container is enlarged, it is difficult to keep good fluidity of the whole toner stored in the toner storing container over a long period of time. If the toner inside the storing container is condensed, the condensed toner may be accumulated in the transport passage for supplying the toner to the developing device, and the speed of transporting the toner may be lowered.
In the structure of Japanese Laid-Open Patent Application No. 61-188564, the development processing part and the toner supplying part are connected together by a pipe in the developing device, and the toner is transported to the development processing part by using the coil screw provided in the pipe.
There is also a structure of different type in which the toner is dropped to the inside of the developing device by its own gravity, without using the coil screw, and the toner is supplied to the development processing part.
However, the above-mentioned structure is attached to the developing device provided in the image forming device and the case in which the toner supplying part is installed in the developing device is included, and the space in which the developing part occupied in the image forming device becomes large, and enlargement and complication of the image forming device are not avoided.
In recent years, effective use of resource materials is demanded, and reuse of the toner collected by the cleaning device which collects the toner remaining on the surface of the photoconductor and the transporting unit is demanded.
In this case, there is a structure in which the toner collected by the cleaning device is temporarily stored in a recovery toner storage device and the stored toner is transported to the toner storing unit or the developing device, or a structure in which a recovery toner discharging part is provided in the cleaning device, and the toner from recovery toner discharging part is transported to the toner storing unit or the developing device.
However, in the case of the image forming device in which the toner collected by the cleaning device is transported to the toner storing unit or the developing device, it is likely to cause enlargement and complication of the image forming device. Generally, the transport of the collected toner between the recovery toner storage device and the toner storing unit is carried out by connecting together the recovery toner storage device and the toner storage unit by using a pipe in which a transporting screw (or coil screw) is provided therein, similar to the transporting unit between the developing device and the toner storing unit.
Namely, in the case of the coil screw, it is necessary to arrange it in the vicinity of the developing device or the recovery toner storage device. And it is necessary to provide a powder transport passage, such as a straight-line transport passage or a curved-line transport passage with a large radius of curvature, in order to ensure accurate and safe rotation of the coil screw.
Thus, if many components are installed inside the image forming device, the degree of freedom of arrangement of the respective components will be reduced because of the layout restrictions in the image forming device, and enlargement and complication of the image forming device will not be avoided.
If the image forming device is enlarged or complicated, the problem of the space for installation of the image forming device arises and the operability in the maintenance of exchange of the toner storing unit etc. gets worse. And there is also a problem that the operation stop time of the image forming device is increased accompanied with the maintenance of the image forming device.
To obviate the problems, there is also proposed a structure in which the toner storing unit is installed outside the image forming device (not the inside of the image forming device) and separately from the developing device, and the powder storing unit and the developing device are connected together by a connecting member, such as a pipe in which a transporting screw is provided inside, so that the toner from the toner storing unit is transported to the developing device. For example, refer to Japanese Laid-Open Patent Application No. 04-198966.
In the case of the above structure, the problem of the operation stop time increase may be reduced by enlarging the storing capacity of the toner storing unit and decreasing the exchange frequency of the toner storing unit.
However, in the structure of Japanese Laid-Open Patent Application No. 04-198966, when the toner storing unit is installed outside the image forming device, the transport passage from the toner storing unit to the developing unit is usually excessively long. If the transport passage of toner is excessively long, the toner may stagnate within the transport passage and a problem that the transporting speed of the toner be decreased may arise. On the other hand, it is also necessary that the supply of toner to the development hopper or the developing device is performed while the toner amount adjustment is performed.
However, if the transport passage of toner is excessively long, it is difficult to perform the supply of toner while performing the toner amount adjustment accurately, and it will be difficult to perform the supply of toner appropriately. That is, it will be difficult to carry out efficient and exact supply of toner from the toner storing unit to the developing device in the case of the structure of Japanese Laid-Open Patent Application No. 04-198966.
Also in the case of the toner storing unit installed inside the image forming device, many components, such as a drive unit of the photoconductor and a drive unit of the developing unit, must be arranged around the developing device. When a large-capacity toner storing unit is used, it is desired to install the toner storing unit at a location distant to some extent from the developing device, the same problem as in the above-mentioned case of the toner storing unit installed outside the image forming device will arise.